DETECTIONS OF CO MOLECULAR GAS IN 24 {mu}m BRIGHT ULIRGs AT z {approx} 2 IN THE SPITZER FIRST LOOK SURVEY

Journal Article · Sat May 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/714/1/100· OSTI ID:21448949

Lin, Yan; Zamojski, M; Dasyra, K M ^[1]; Tacconi, L J; Lutz, D ^[2]; Fiolet, N; Omont, A ^[3]; Sajina, A ^[4]; Neri, R; Cox, P ^[5]

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1. Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125 (United States)
2. Max-Planck Institut fuer Extraterrestrische Physik (MPE), Giessenbachstrasse, D-85741 Garching (Germany)
3. UPMC University of Paris 06, UMR7095, Institut d'Astrophysique de Paris, F-75014, Paris (France)
4. Haverford College, Haverford, PA 19041 (United States)
5. Institut de Radio Astronomie Millimetrique (IRAM), St. Martin d'Heres (France)

We present CO observations of nine ultra-luminous infrared galaxies (ULIRGs) at z {approx} 2 with f{sub {nu}}(24 {mu}m) {approx_gt} 1 mJy, previously confirmed with the mid-IR spectra in the Spitzer First Look Survey. All targets are required to have accurate redshifts from Keck/GEMINI near-IR spectra. Using the Plateau de Bure millimeter-wave Interferometer at the Institute for Radioastronomy at Millimeter Wavelengths, we detect CO J(3-2) (seven objects) or J(2-1) (one object) line emission from eight sources with integrated intensities I{sub c} {approx} 5{sigma}-9{sigma}. The CO-detected sources have a variety of mid-IR spectra, including strong polycyclic aromatic hydrocarbon, deep silicate absorption, and power-law continuum, implying that these molecular gas-rich objects at z {approx} 2 could be either starbursts or dust-obscured active galactic nuclei (AGNs). The measured line luminosity L'{sub CO} is (1.28-3.77) x 10{sup 10} K km/s pc{sup 2}. The averaged molecular gas mass M{sub H{sub 2}} is 1.7 x 10{sup 10} M{sub sun}, assuming CO-to-H{sub 2} conversion factor of 0.8 M{sub sun} (K km/s pc{sup 2}){sup -1}. Three sources (33%)-MIPS506, MIPS16144, and MIPS8342-have double peak velocity profiles. The CO double peaks in MIPS506 and MIPS16144 show spatial separations of 45 kpc and 10.9 kpc, allowing the estimates of the dynamical masses of 3.2 x 10{sup 11} sin{sup -2}(i) M{sub sun} and 5.4 x 10{sup 11} sin{sup -2}(i) M{sub sun}, respectively. The implied gas fraction, M{sub gas}/M{sub dyn}, is 3% and 4%, assuming an average inclination angle. Finally, the analysis of the Hubble Space Telescope/NIC2 images, mid-IR spectra, and IR spectral energy distribution revealed that most of our sources are mergers, containing dust-obscured AGNs dominating the luminosities at (3-6) {mu}m. Together, these results provide some evidence suggesting submillimeter galaxies, bright 24 {mu}m, z {approx} 2 ULIRGs, and QSOs could represent three different stages of a single evolutionary sequence, however, a complete physical model would require much more data, especially high spatial resolution spectroscopy.

• OSTI ID: 21448949
• Journal Information: Astrophysical Journal, Vol. 714, Issue 1; Other Information: DOI: 10.1088/0004-637X/714/1/100; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ENERGY SPECTRA
GALACTIC EVOLUTION
GALAXIES
GALAXY NUCLEI
HYDROGEN
INCLINATION
INFRARED SPECTRA
INTERFEROMETERS
LUMINOSITY
POLYCYCLIC AROMATIC HYDROCARBONS
RADIOASTRONOMY
RED SHIFT
SILICATES
SPATIAL RESOLUTION
SPECTROSCOPY
TELESCOPES
AROMATICS
ASTRONOMY
ELEMENTS
EVOLUTION
HYDROCARBONS
MEASURING INSTRUMENTS
NONMETALS
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RESOLUTION
SILICON COMPOUNDS
SPECTRA